Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.33	8.647%	$91.622	$91.62	$91.60	$91.60
Purchase #2	$168.74	5.724%	$178.3987	$178.40	$178.40	$178.40
Purchase #3	$170.31	5.397%	$179.5016	$179.50	$179.50	$179.50
Purchase #4	$189.96	10.145%	$209.2314	$209.23	$209.25	$209.20
Purchase #5	$16.26	11.401%	$18.1138	$18.11	$18.10	$18.10
Purchase #6	$204.71	9.217%	$223.5781	$223.58	$223.60	$223.60
Purchase #7	$94.60	9.829%	$103.8982	$103.90	$103.90	$103.90
7 purchase totals =	$928.91		$1,004.3438	$1,004.34	$1,004.35	$1,004.30